Screen printing machines

ABSTRACT

A quick release pallet for a screen printing machine in which the pallet has locating recesses at either ends which locate the pallet on the pallet arm of the screen printing machine by engaging locating lugs on the pallet arm. A toggle clip secures the pallet in position. The advantages are that the pallet has no attachments and can be very quickly positioned and released. Because there are no screw holes in the top surface of the pallet it has a larger print area. The pallet can also be modified to a vacuum pallet with a perforated top plate and a vacuum manifold below.

This application is a continuation in part to application Ser. No.09/359,115, filed Jul. 23, 1999, now U.S. Pat. No. 6,237,488.

This invention relates to improvements in screen printing machinesparticularly to the pallet and pallet arm constructions used in suchmachines.

BACKGROUND TO THE INVENTION

Garments such as tee shirts are decorated using multi printing head,screen printing machines. The number of heads correspond to the numberof colours to be printed. U.S. Pat. No. 3,795,189 [Jaffa] and U.S. Pat.No. 5,031,527 [Eppinger] disclose examples of the type of machines usedin printing garments.

The garments are supported on a pallet, which in turn is supported, forregistry with the printing head, on a pallet arm. The pallet is movedsuccessively past the desired number of printing heads until theprinting is complete. Different size garments require correspondinglydifferent sized pallets. Usually pallets are of the same length but varyin width from a garment sleeve width to a large body width. This meansthat the pallets need to be removed from the pallet arms on a frequentbasis.

The positioning of the pallet on its pallet arm needs to be precise andsecure to ensure that registration with successive printing heads ismaintained.

Conventionally one means of removably securing pallets to pallet armshas been to use 2 or 3 counter sunk screws at each end of the pallet.This is quite adequate in terms of registration accuracy and retentionof alignment but involves extensive labour time to fit a new set ofpallets to a machine. A number of quick release mechanisms have beenproposed. Some use a key and keyhole type arrangement where either thepallet or the pallet arm has a keyhole slot and the other has acomplementary waisted head that can be locked into the narrow part ofthe slot. Another quick release means relies on the use of a rail andcomplementary track arrangement with either the pallet or the pallet armhaving a rail and the other having a channel track of complementarycross section to the rail and a securing means to lock the two relativeto one another for registration relative to the length of the arm. Inmost of these devices several wing nuts or bolts need to be tightened tosecure the aligned pallet to the pallet arm.

U.S. Pat. No. 4,031,825 [Jaffa] discloses a pallet which fitssleeve-like over the pallet arm and is held in place by springs in theside edges of the pallet arm. Even though the pallet appears to besimple it needs to be fabricated or machined extensively as does thepallet arm.

U.S. Pat. No. 5,592,877 in part discloses a pallet which can beinstalled and released quickly and utilises a pneumatic releasemechanism to free the pallet. The pallet comprises two plates screwedtogether with the lower plate having lugs and slots that cooperate withrecesses and a pin in the pallet arm to locate the pallet.

Although these quick release arrangements are an improvement they dohave short comings in terms of convenience and operator simplicity. Alsothey all involve additional manufacturing steps in preparing thepallets.

It is desirable that a pallet be adapted for use with a vacuum systemwhich creates a vacuum through the surface of the pallet to retain thegarment in position during the printing process.

BRIEF DESCRIPTION OF THE INVENTION

To this end the present invention provides, in a screen printing machineof the type having a pallet mounted on a pallet arm which issuccessively brought into registry with a series of printing heads theimprovement comprising

a) a pallet having a longitudinal axis and leading and trailing edgeportions extending laterally at each end of the longitudinal axis;

b) a pallet arm to support said pallet along its longitudinal axis;

c) at least one edge recess in either the leading or trailing edge ofsaid pallet and at least one location recess in or adjacent to the otherof said leading or trailing edges;

d) at least one fixed locating stop on said pallet arm adapted to fitsaid at least one edge recess; and

e) at least one locating means mounted on said pallet arm remote fromsaid at least one fixed locating stop, said locating means being ofcomplementary shape to said at least one location recess in or adjacentto said leading or trailing edge of said pallet.

The pallet of this invention is unique in that it is an integral palletdevoid of parts welded or otherwise fixed to it and having no fixingholes or recesses in its upper surface.

In contrast to prior art quick release systems, the pallet of thisinvention requires no additional device or protrusion to be weldedmounted or adhered to its surface. The only precision machining requiredis to machine recesses into the edge of one end of the pallet and intothe opposite edge or the base of the pallet adjacent the opposite edge.The pallets can in other respects be of the same shape and materials asis conventional for screen printing pallets.

Although two location points are adequate it is preferred to use 3points. Preferably one adjustable point is located at the free end ofthe pallet arm and two adjacent the leading edge of the pallet when itis secured to the pallet arm. The recesses in the edges may be into theedge or into the top surface of the pallet at the edge. If the locatingrecess is into the base of the pallet it is preferably into underneathsurface of the pallet adjacent the trailing edge and shaped to fit overa lug or bolt head protruding from the surface of the pallet armadjacent its free end.

In order to press the pallet securely into its register position thesurfaces of the recesses and the corresponding contact surfaces of thelocating stops on the pallet arm are angled in complementary fashion sothat the pallet is pressed along its longitudinal axis and also pressedonto the pallet arm. The final securing force can be provided by aspring clip or toggle clamp acting on the edge of the pallet oppositethe edge which abuts the fixed stops on the pallet arm.

To fit the pallet, it is simply placed onto the pallet arm so that thelocating stops are aligned with the recesses and then the spring clip ortoggle is locked into place.

Only one fastening action is needed in contrast to the need to fastenseveral bolts in the prior art devices. Because there are no screw orbolt holes in the top surface of the pallet, a larger surface area ofthe pallet is available for printing than is the case for prior artpallets. Because there are no protrusions or rails mounted on the palletas is the case with prior art quick release pallets, the pallets of thisinvention pack flat and are easier to store, transport and clean.

In a modification of the pallet of this invention the pallet is adaptedfor use with a vacuum manifold. The pallet is formed in two parts theupper surface being perforated to enable air flow through the surfaceand the lower surface incorporating a recess communicating with a vacuumoutlet connected to a manifold. The manifold may be a third part of thevacuum pallet or it can be a part of the pallet arm which mates with thepallet.

The present invention in a further aspect provides a pallet forsupporting an item to be screen printed having

a) a longitudinal axis and leading and trailing edge portions extendinglaterally at each end of the longitudinal axis;

b) a perforated top plate

c) a recessed bottom plate adapted for connection to a vacuum line

d) at least one edge recess in either the leading or trailing edge ofone or both of said top plate and said bottom plate

e) at least one location recess in or adjacent to the other of saidleading or trailing edges in either or both the top plate and saidbottom plate

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of this invention will now be described withreference to the drawings in which

FIG. 1 is an isometric view of the assembled pallet arm and pallet ofthis invention;

FIG. 2 is a view of the pallet arm;

FIGS. 3A and 3B are views of the upper and lower surfaces of the palletof this invention;

FIG. 4 is a sectional view of the pallet and pallet arm of a secondembodiment of this invention and;

FIG. 5 is a partial exploded view of the leading edge of the pallet andits associated pallet arm of the same embodiment as shown in FIG. 4.

FIG. 6 is a side elevation of a screen printing machine incorporating avacuum line for applying a negative air pressure to the upper surface ofthe pallets;

FIG. 7 is a plan view of a vacuum pallet of this invention;

FIG. 8 is a side view and detail along the line A—A of the pallet ofFIG. 7;

FIG. 9 is a detailed plan view of the perforated top plate of the palletof FIG. 7;

FIG. 10 is a detailed plan view of the bottom plate of the pallet ofFIG. 7;

FIG. 11 is a plan view of a manifold used in the pallet of FIG. 7;

FIG. 12 is a side view of the manifold of FIG. 11.

The pallet 10 is a flat aluminium cast plate of a size matched to thegarment to be printed. The pallet has an upper surface 12 and a lowersurface 11. The leading edge incorporates two recesses 13 ofsemicircular shape with chamfered or inclined faces 14. The trailingedge incorporates a clip recess 16. On the underneath surface adjacentthe trailing edge is the location or key recess 15. The recess 15 iscentred over the longitudinal centre line of pallet 10 which passesthrough the mid point between the recesses 13.

The pallet arm 20 has an upper surface 21 and a side portion 22. Countersunk bolt heads 24 protrude from the upper surface 21 of the pallet arm20. The bolts 24 can be adjustable in height above the surface 21 and onthe under sides of the screw heads 24 are inclined faces 25 which engagethe surfaces 14 of the recesses 13 in pallet 10. Adjacent the free endof the pallet arm is the key protrusion 26 preferably of plastic andscrewed into the surface 21 so that it can be removed. The protrusion 26is slightly shorter in length than the corresponding locating recess 15on the underside of pallet 10. The protrusion 26 is preferably centredon the longitudinal centreline of the pallet arm which centre line alsopasses through the midpoint between the stops 24.

Under the free end of the pallet arm 20 is the preferred lockingmechanism a toggle clip comprising the over centre toggle arm 27 and theclip 29. The end 28 of clip 29 seats in the recess 16 of pallet 10. Theportion 30 of clip 29 engages underneath edge of the pallet arm surface21 to exert spring pressure onto the edge recess 16 of pallet 10. Thecurved portion 31 of clip 29 applies a longitudinal force to thetrailing edge of pallet 10 via the end 28 of the clip 29 engaging therecess 16. These two forces ensure that the pallet 10 is held securelyin registry with the centre line of arm 20.

The side 22 has a portion 23 cut away at the free end of arm 20 toimprove access to the toggle 27 and clip 29. The clip end 28 is placedinto engagement with the recess 16 of pallet 10 and the toggle 27 closedto lock the pallet into position. By making fine adjustments to theheight of the screws 24 the longitudinal alignment of pallet 10 can beadjusted.

Instead of the toggle mechanism a spring loaded stop can be located onthe free end of the pallet arm which engages a recess in the centre ofthe pallets trailing edge. In such an arrangement the protrusion 26 andrecess 15 may not be needed. The pallet in that construction would bepressed against the spring stop to locate the stops 24 in recesses 13and then released so that the spring would press the pallet intoposition.

The recesses 13, 15 and 16 in the pallet are all subject to wear. Thewear surface may be incorporated In a plate which fits within a recessin the pallet so that the surface of the pallet and the adjacentsurfaces of the plate are flush. This enables the wear surfaces of thepallet to be replaced when wear affects their function. The platescontaining the recesses 13, 15 and/or 16 may be secured to the plate bycounter sunk screws or adhesives.

In the embodiment shown in FIGS. 4 and 5 an alternative fixingarrangement is shown. The pallet 35 is held to the pallet arm 40 at twopositions. The leading edge of pallet 35 has a rectangular inclinedrecess 38 which incorporates a centering groove 39. The pallet arm 40has stop 47 with an inclined facing edge 50 which engages the inclinedrecess 38 of pallet 35. The pin 49 on stop 47 engages the centeringgroove 39. The stop 47 is fixed to the pallet arm by the counter sunkscrews 48.

The second securing position is shown in FIG. 4 where recesses 36 in theundersurface of pallet 35 are engaged by the grips 42. The recesses 36incorporate in the inner edges wedged grooves 37 which are engaged bythe wedged ribs 43 on the grips 42. The grips 42 are mounted on thepallet arm 40 by a screw threaded shaft 41. Rotation of the shaft 41 byturning handle 44 tightens or loosens the grips 42. This alternativeneed not have any clamp on the trailing edge of the pallet. The pallet35 is placed over the pallet arm 40 so that the grips 42 enter therecesses 36, then the pallet is urged against stop 47 so that pin 39fits in groove 39 and then the grips are tightened by turning handle 44so that the ribs 43 are urged into the grooves 37.

FIG. 6 Illustrates a typical screen printing machine having print heads101 which rotate with the central support 102 and print garments loadedon pallets 112. The pallets 112 are supported on pallet arms 111. Themachine control panel 106 is situated at the load/unload stations whichdon't have associated print heads. The vacuum pallet 112 is connected toa vacuum line 107 which communicates with the central vacuum region 108within the central support 102. The vacuum region 108 is connected to avacuum pump [not shown] via the external line 109.

The vacuum pallet 112 as shown in FIGS. 7 to 12 consists of a top plate121 as seen in detail in FIG. 9 with a grid of perforations 122 tocreate an even suction on the top surface of the top plate 121. This topplate has the two semi circular edge recesses 13 at one end and the cliprecess 16 in the other end. The top plate 121 sits on the bottom plateand may be made from cold rolled aluminium or rubber.

The bottom plate 126 as seen in detail in FIG. 10 has a series oftransverse slots or channels 127 into the surface to provide air flowchannels from the perforations in the top plate. The holes 128 in thechannels 127 provide air flow communication to the manifold 131. Thefastening holes 129 are for screws or bolts to attach the two manifolds131 to the base of the bottom plate 126. The bottom plate alsoincorporates the semicircular location recesses 13 at one end and theclip recess 16 at the other end. The bottom plate 126 is preferablymachined from Aluminium tooling plate.

Each manifold 131 as shown in FIGS. 11 and 12 comprises a channelsection 132 dimensioned to cover one of the rows of air holes 128 in thebottom plate. The fastening holes 133 correspond to the fastening holes129 in the bottom plate. The vacuum outlet hole 134 in the channel 132is adapted to receive the end of the vacuum line 107. The manifold 131is preferably machined from Aluminium.

From the above description it can be seen that this invention provides

1) a pallet that is simple to machine with no added devices orprotrusions.

2) The pallet is simple to assemble to the pallet arm.

3) The pallet has a larger free surface for printing because there areno screw holes through its top surface

4) The pallet and arm can be made from off the shelf components whichreduces the costs of production.

5) The pallet is adapted for use with a vacuum line.

What is claimed is:
 1. In a screen printing machine of the type having apallet mounted on a pallet arm which is successively brought intoregistry with a series of printing heads the improvement of a pallet andpallet arm combination comprising: a) a pallet having a longitudinalaxis and leading and trailing edge portions extending laterally at eachend of the longitudinal axis, and an upper surface and a lower surfaceopposed to said upper surface; b) a pallet arm to support said palletalong its longitudinal axis; c) at least one edge recess in either theleading or trailing edge of said pallet and at least one location recessin or adjacent to the other of said leading or trailing edges; d) atleast one fixed stop on said pallet arm adapted to fit said at least oneedge recess; and e) at least one locating means mounted on said palletarm remote from said at least one fixed stop, said locating means beingof complementary shape to said at least one location recess in oradjacent to said leading or trailing edge of said pallet f) said palletincluding perforations in its upper surface communicating with a vacuumline associated with said pallet arm.
 2. A pallet for supporting an itemto be screen printed comprising: a) a longitudinal axis and leading andtrailing edge portions extending laterally at each end of thelongitudinal axis; b) a perforated top plate; c) a recessed bottom plateadapted for connection to a vacuum line; d) at least one edge recess ineither the leading or trailing edge of one or both of said top plate andsaid bottom plate; and e) at least one location recess in or adjacent tothe other of said leading or trailing edges in either or both the topplate and said bottom plate.